Where Mindful Learning Begins
Where Mindful Learning Begins
Class 10 Science NCERT Solutions Chapter 8 (CBSE 2026-27) — every in-text question, every embedded Activity question, and all 4 back-of-chapter Exercises on this one page, solved with the reasoning behind each answer.
Heredity follows directly from Chapter 7 and asks how the variations created during reproduction actually get passed down and expressed. It moves from how variation accumulates across generations, into Mendel's landmark pea plant experiments — the surprising disappearance and reappearance of traits that revealed dominant and recessive genes, and the independent inheritance of separate traits like seed shape and seed colour — and finally to how sex is genetically determined in humans through the X and Y chromosomes. It's a short but concept-dense chapter, and these NCERT solutions work through every Activity-based question and the full Exercise set in detail, including the genetics reasoning behind each answer.
Heredity picks up exactly where Chapter 7 left off: reproduction creates variation, so what happens to that variation as it passes down through generations? The chapter first shows that variation keeps accumulating — each new generation carries both what it inherited and newly created differences — and that not all variations survive equally well, which is the seed of the idea of evolution. It then turns to Gregor Mendel's pea plant experiments, which is really the heart of the chapter: crossing tall and short plants produced only tall offspring in the first generation, but short plants reappeared a generation later in a 3:1 ratio, revealing that every individual carries two copies of each trait, that one copy (dominant) can mask the other (recessive), and that separate traits like height and seed shape are inherited independently of each other. The chapter closes by explaining how this same machinery — genes packaged into chromosomes, one set from each parent — determines something as fundamental as a child's sex, through the X and Y chromosomes. Every question woven through the chapter is solved here, section by section, in the order the textbook presents it: the two "QUESTIONS" boxes after Sections 8.1 and 8.2, the questions embedded directly inside Activities and figures, and the full 4-question Exercise set at the end.
How small differences build up across generations, and why environmental selection of variants underlies the survival of a species over time.
Dominant and recessive traits, the 3:1 and 1:2:1 ratios in F2 generations, and the independent inheritance of separate traits like height and seed shape.
How X and Y sex chromosomes, one from each parent, determine whether a human child is born a boy or a girl.
Trait B (present in 60% of the population) is likely to have arisen earlier. In an asexually reproducing population, a trait that arose earlier has had more generations to spread through continued reproduction, so a higher percentage points to an earlier origin — while trait A, present in a smaller fraction, likely arose more recently and has had less time to spread.
Variations increase diversity within a population, meaning different individuals may have different characteristics or advantages. If environmental conditions change (e.g., a rise in temperature, a new disease, scarcer resources), individuals with variations suited to the new conditions are more likely to survive and reproduce, while those without such variations may not. This increases the chances that at least some individuals of the species will survive changing conditions, promoting the survival of the species as a whole.
When Mendel crossed tall and short pea plants, all F1 (first-generation) offspring were tall — no medium-height plants, and the short trait seemed to vanish. But when the F1 tall plants were self-pollinated to produce F2 offspring, about one-quarter of the F2 plants turned out short. This showed the short trait hadn't been lost in F1 — it had been inherited but not expressed (hidden), while tallness was expressed. This demonstrated that tall (T) is dominant (expressed even with just one copy) and short (t) is recessive (expressed only when both copies are the recessive form, i.e., tt).
When Mendel crossed a tall, round-seeded plant with a short, wrinkled-seeded plant, the F1 offspring were all tall with round seeds. Self-pollinating these F1 plants to get F2 offspring produced mostly tall-round and short-wrinkled plants (like the parents), but also some new combinations — tall with wrinkled seeds, and short with round seeds. These new combinations appearing in F2 showed that the gene for height and the gene for seed shape are inherited independently of each other, rather than always being inherited together as a fixed pair.
Yes — this is enough to conclude that blood group O is recessive (and A is dominant). Since the daughter has blood group O, she must have inherited an O gene from both parents. Since her father's blood group is A, he must be carrying one copy of the O gene (passed to his daughter) alongside a copy of the A gene — yet his own blood group is expressed as A, not some mixture. This means the A trait is masking/dominant over the hidden O trait he also carries, showing A is dominant over the recessive O.
The sex of a child is genetically determined by the sex chromosomes inherited from the parents. Women have two X chromosomes (XX), while men have one X and one Y (XY). Every child inherits an X chromosome from the mother. The father's contribution decides the sex: an X from the father gives a girl (XX); a Y from the father gives a boy (XY).
Such surveys typically find that the free earlobe trait is dominant, while the attached earlobe trait is recessive. This means a person needs only one copy of the "free earlobe" gene version to have free earlobes, but needs two copies of the "attached earlobe" gene version to have attached earlobes.
Since TT and Tt plants both look tall (identical in appearance), a visual count alone can't tell them apart. To confirm the 1:2:1 genetic ratio, each tall F2 plant can be self-pollinated (or test-crossed with a homozygous recessive short (tt) plant) and its offspring observed: a TT plant produces only tall offspring, while a Tt plant produces a mixture of tall and short offspring (roughly 3:1 on self-pollination, or 1:1 in a test cross with tt). This distinguishes which "tall" F2 plants are TT and which are Tt, confirming the 1:2:1 ratio.
Since the F1 progeny of round-green × wrinkled-yellow parents are all round and yellow, this shows that round (R) and yellow (Y) are the dominant traits, while wrinkled (r) and green (y) are the recessive traits.
In asexually reproducing organisms, since there is only a single parent, the offspring receives the complete set of genetic material from that one parent through DNA copying — there is no combination or segregation of genes from two different parents. As a result, the offspring is nearly identical to the parent, with only small variations arising from minor inaccuracies in the DNA-copying process itself, rather than through the shuffling/recombination of genes from two parents, as happens in sexual reproduction.
Answer: (d) TtWw
Since all progeny are violet-flowered (with no white progeny appearing), violet (W) behaves as dominant. Since the tall parent, crossed with a short (tt) parent, produced roughly half short progeny — a result that only happens if the tall parent is heterozygous for height (Tt), not homozygous (TT), since a TT × tt cross would give 100% tall offspring, not a ~1:1 tall:short split. This makes the tall parent's genotype TtWw.
No, this information alone isn't enough. Children with light-coloured eyes tending to have parents with light-coloured eyes is simply consistent with the trait being inherited — but this pattern would show up whether the trait is dominant or recessive. To determine dominance, we'd need more information, such as what happens when a light-eyed and dark-eyed individual have children, or whether the trait can "skip" a generation and reappear after being masked (the hallmark of a recessive trait), as Mendel tracked across his pea plant generations.
Through the process of meiosis during the formation of germ-cells (sperm and egg) in each parent. This special cell division reduces the number of chromosomes in the germ-cells to exactly half the normal number found in the body's other cells. When the male germ-cell (sperm) and female germ-cell (egg) — each with half the normal chromosome number — fuse during fertilisation, the full normal chromosome number is restored in the offspring, with exactly half of the chromosomes (and genetic material) coming from the father and half from the mother, ensuring an equal genetic contribution from both parents.
Next up is Chapter 9 — Light: Reflection and Refraction, moving into the physics portion of the syllabus. Or explore the full chapter list, browse the Class 10 Science hub, or book a free demo class for personalised coaching.
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